This invention relates to the large scale processing of water for urban, industrial or agricultural use and also to the production of electrical power. More particularly the invention relates to methods and apparatus enabling an advantageous combining of these formerly separate operations in installations where former waste products of one operation may be utilized in the other.
As a serious shortage of usable water exists in many regions, increased efforts are being made to expand and improve water supply operations and to reclaim and reuse waste water. In most urban and industrial areas water from natural sources must be imported and must be treated to assure that it is suitable for human consumption although much of the water is not ultimately used for that purpose. Following usage, the water enters a sewage system and immediately becomes a serious disposal problem as it is contaminated with particulate matter, bacteria and viruses and the like. Concern over environmental pollution has made it necessary to perform costly further operations simply to convert the sewage water into a form suitable for discharge into rivers and oceans. Recovery of such waste water for reuse, using known technology, is an extremely costly process. The problems of water management have been still further complicated with the recent realization that chlorination of water may itself contribute to the formation and accumulation of toxic chemicals in water supplies.
Thus very costly installations and operations are needed to transport and treat water which for the most part is used only once after which the end product is waste water which is itself costly to dispose of.
Water management must take agricultural needs into account to a greater extent than has heretofore been the case. Population growth has outstripped the food production capabilities of existing agricultural lands. It is well recognized that the productivity of farm lands must be increased and that it would be highly desirable to enable the growing of crops on lands which are not presently considered suitable for this purpose. Primarily, this is a matter of providing irrgation water and plant nutrients for regions where these are not presently available in sufficient quantities. There is much unused land, notably in arid regions, which could potentially produce food. Large scale conversion of such land to productive agricultural use, using known techniques, is often not economically feasible at this time.
Considering now another and seemingly unrelated resource problem, there have recently been shortages of electrical energy for utility purposes. Much electrical power production is realized with generators driven by steam powered turbines. The steam is usually produced by burning fossil fuels although lately there has been considerable interest in expanding usage of geothermal steam sources.
In steam driven power systems, it is not possible to convert the total energy content of the steam to electrical power, typical conversion efficiencies being well under 50%. A very substantial portion of the steam energy content cannot be recovered as electric power in conventional systems. The expanding steam drives the turbine. When the steam has too little remaining energy to exert the necessary force on the turbine blades, it must be vented or condensed and the heat of vaporization, which may be more than half of the original content of the steam is thereby wasted. It is not only wasted, but in fact presents a very serious disposal problem. In most cases such steam cannot be simply discharged, but must be condensed. This requires large amounts of cooling water or very costly equipment to disperse the heat which has been extracted from the steam in the condensation process. Discharged hot cooling water may in turn cause environmental problems. Thus a parallel with the water management problem may be seen. Much of a potentially useful product, heat energy in this case, is unutilized and in fact presents a disposal problem.
Under-utilization of steam resources is not limited to the loss of thermal energy from turbine discharge steam as discussed above. There are potential steam sources for power generation plants which cannot readily be used with existing technology. Many geothermal steam sources, for example, are not readily usable because of a relatively low energy content in comparison with steam produced in a boiler by burning fossil fuels or because of the presence of highly corrosive contaminants such as brine that cause rapid deterioration of turbines and other power station components.
Thus, there are scarcities of many resources including usable water, productive farm land and electrical power. The existing technologies for resolving these problems require extremely costly equipment and operations while being inefficient in the sense that much of the desired end product is not only wasted but also creates a costly disposal problem.
In some regions, each of the problems discussed above not only exist side by side but have become extremely critical. In southern California, for example, there is a very large and growing urban area with increasing demands for electrical power, usable water and food that cannot be satisfied from local resources using known technology. Concurrently, the problem of disposing of sewage water and discharged thermal energy from power generation facilities in this region have become severe. Adjacent this metropolis is a sparsely populated desert with undeveloped geothermal energy reserves and having soils and climatic conditions suitable for highly productive agricultural operations if water and plant nutrients are made available.
Much effort is being devoted to resolution of each of the problems discussed above, but each has been treated as a separate activity having little relation to the other. It has not been recognized to any great extent that combined solutions are possible in which the waste products or rejected resources of one such operation may be converted into valuable raw material for another. This is due, at least in part, to a lack of practical processes and apparatus for effecting such integrations.